This chapter describes the standard IEC 61850 which is a communication protocol for electrical devices used in substations. This uses the sampled values and GOOSE protocols which are mapped directly to the data link layer for reduced protocol over-head. In this chapter, IEC 61850 standard is discussed including parameters for sam-pled rate of analogue values, configurable for content of dataset.
sampled values are important in electrical parameters they are beneficial in such a way that they enable sharing of values, transmit sampled analogue and digital val-ues, sending of data in data link layers, interference and providing time coherent SMV. The sampling rates are defined in this chapter as the transmission speed is 100 Mb/s so 80 samples per period for protection application.
Testing of multifunctional distance protection devices is also discussed in this chap-ter. The measurement of active, reactive and apparent power or power factor are often available from the relays when they are required in the substation automation
system. Another technique is explained here which is quadrilateral relay algorithm and protection. It includes the calculation of bandwidth. The algorithm of distance relay required input signals which are harmonic magnitude, phase of three voltage and current signals each, zero sequence magnitude and phase current to measure phase quantities.
Relay characteristics and impedance diagram play an important role in measuring the values of electrical parameters. Distance relay has a feature of inherent remote back up functionality. Its resistive coverage is better than any mho type character-istic for short lines. The quadrilateral charactercharacter-istic is the most appropriate for the earth fault impedance measurement while the polygonal impedance characteristics are highly flexible in terms of fault impedance coverage for both phase and earth faults. Omicron is a testing device used for the testing of IEDs functionality and offers the IEC 61850 communication. The delay time of SMV can be defined by the number of hops in a network, internal application delay of protection, store and for-ward latency, theoretical maximum delay, recommended max delay setting and a new term named queue latency. The queue latency is defined as when the port has started to send a full sized frame before SMV frame and switch has been configured to prioritize SMV. Another precaution is important to reduce error which is network packet analysis to make safe the packet traffic.
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Chapter 3
THE AIMS OF THE DISSERTATION
The objectives of the dissertation are as follows:
• Defining the protection function algorithms.
• Creating a Simulink model for distance relay protection which can define the fault type, fault impedance and total harmonic distortion.
• Evaluation of harmonic impact on the digital relays and comparing the protec-tion model with a physical digital relay.
• Testing the merging units of the digital relay and Omicron device in the lab-oratory and compare the functions and timing analysis. By using neural net pattern recognition, we could find the relation between the inputs (number of samples/ms—interval time between the packets) and the source of the data.
• Developing real time application that subscribes the data stream coming from a station near protection laboratory in Brno University of Technology. IEC 61850-9-2 LE SMs are used to transmit the traffic to university laboratory with 16 km of fiber optic cable . The application built using MATLAB and can read the traffic from the ethernet port, the traffic decoded and convert from ASCII to the decimal numbers then draw the current and voltage values. The appli-cation developed without using any need for additional hardware.
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Chapter 4
THE IMPACT OF CURRENT
TRANSFORMER SATURATION ON THE DISTANCE
PROTECTION
The distance protection relay calculates the voltage and current at the relay location and evaluates the ratio between these quantities. Distance relays are widely used on transmission and even distribution systems. Current transformers (CT) are the very important part of the power system protection. The main purpose of a CT is to transform the primary current in a high voltage power system to single level that can be handled by delicate electronic device. This chapter deals with the influence of CT saturation on distance digital relay. Saturation of the CT is evaluated for fault close to the relay location.
4.1 THE EXCITATION CURVE OF CTS
The electrical power system has many elements which are important to ensure se-curity and protection of the system. The current transformer is a device which is connected to the power system and is used to produce low current that is possible to use in protection devices. The current transformer has two parts (primary and secondary). The primary side has few coil turns and the secondary side has a large coil turns. This structure is used to obtain low current on the secondary side; the current which is produced in secondary side is used for several functions in power system such as metering and protection, therefore, the output current of the current transformer becomes the input for the protection device, however, the ratio between the primary winding and the secondary winding have caused the current saturation during faults which occurs in the transmission line. In this case, the relay which is connected to the current transformer cannot respond or trip in right way [47]. The current transformer is used for different functions as was mentioned above (meter-ing and protection), however, the level of accuracy depends on the operation type.
There is a relationship between the accuracy of the CT and rated current and the good accuracy is important for metering [77].
4.1.1 CHARACTERISTICS OF CURRENT TRANSFORMER
The current transformer primary winding is connected in series with the device in which the current is to be measured. Since current transformer is fundamentally
a transformer, it transmits the current from the primary to the secondary side, in-versely proportional to the turns so as (4.1):
Ip =n×Is (4.1)
wherenis the ratio of turns between the secondary and primary winding.
The equation (4.1) explains the normal transformer with a different number of wind-ings between the primary and secondary side. Figure 4.1 explains the equivalent circuit for a current transformer. ReactanceXm explains the magnetizing current;
the secondary current which is generated in secondary side is divided into internal current and magnetizing current. CurrentIsrepresents the internal winding current.
FIGURE4.1: Equivalent circuit for a current transformer [52]
4.1.2 SATURATION TEST
The current transformer can be tested as connected the secondary side to the voltage source then measured the current which produced on the secondary side, taking into consideration that the primary side remains open without load during the test. The voltage increased gradually with measuring the current until reach to the saturation point which is started when the voltage increased 10 % and the secondary current increased 50%. After this point, any small increase in voltage has resulted in large increases in current that supposed to mean the saturation started [45]. Thane test starts with decreased the voltage value gradually and writing the current value for all voltage values until the voltage value becomes at the end is equal zero to make sure that core. Demagnetization after that we can draw the magnetic curve [46] [55].
4.1.3 AC SATURATION
The alternative current had resulted in producing the alternative magnetic flux. The flux is proportional to the secondary current, consequently, when the current in-creased, the flux increased too as shown in figure 4.2. The saturation has appeared when the current increased to the high value (faults), then the flux increased to the high value which the iron core not able to afford this flux [49] [52]. This equation explains the relationship between the different parameters which create the current saturation curve and the specific domain that is allowed for the current transformer to work without saturation , however, there are details about the ratio between in-ductance and resistance which is major parameter to define the saturation curve, in
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FIGURE4.2: Secondary excitation curve TABLE4.1: Excitation curve values [55]
Ve(volt) Ie(amper) Ze(ohm)
3 0.001 3000
7.5 0.002 3750
12.53 0.003 4167
18 0.004 4500
60 0.01 6000
150 0.02 7500
200 0.025 8065
300 0.05 6000
400 0.2 2000
447 1 447
486 10 49
general, the current transformer has maximum fault current which can be applied in protection without saturation after this maximum value the current saturation appears [50] [51].
Bs·N·A·ω= χ
R·If ·ZB (4.2)
Moving to the equation to explain how we can avoid the current saturation in the current transformer by observing the ratio between the major parameters If fault current, the ratio of reactance and resistance and current transformer burden. In equation (4.3) we assumed that the voltage is 20 times between primary and sec-ondary:
20≥(χ
R +1)·If ·ZB (4.3)
whereIf is the fault current in current transformer;ZB is the burden impedance andX/Ris the ratio of reactance and resistance.
FIGURE4.3: Secondary current of transformer with CT saturation